I. Field of the Invention
This invention relates generally to implantable electronic tissue stimulating devices, and more particularly to the physical packaging of the electronic circuitry used in such devices in which circuit boards carrying hybrid circuitry are interconnected with flexible printed conductors, allowing the boards to be juxtaposed by folding the flexible interconnecting conductors.
II. Discussion of the Prior Art
The miniaturization of electronic devices has resulted in a widespread use of flexible printed circuit boards and interconnecting cabling. The use of flexible printed circuitry can minimize the space required to accommodate interconnected electronic circuits. The printed circuit boards are usually fitted into an hermetically sealed, moisture-impervious housing of such devices as pacemakers, defibrillators, neurostimulators, hearing aids and other small electronic devices. Typically, limits are imposed on the construction of the flexible printed circuit boards because of volume restrictions imposed by the allowable size of the housing of the implantable device in which the circuitry is contained.
Taking as an example a small electronic device, such as an implantable defibrillator, it typically requires a hybrid circuit including discrete and integrated circuit components that must be connected to and contained within a hermetically sealed housing with a battery power supply and energy storage capacitors. In prior art designs, the hybrid circuit is typically disposed on a multi-layer circuit board with active and passive circuit components mounted on the opposed major surfaces of the printed circuit board. While this approach generally permits an increased component count-per-unit volume occupied, it tends to increase the cost of manufacture in that multiple passes with pick-and-place machines are needed to populate both sides of the printed circuit boards with components.
It is known in the art to provide multiple printed circuit boards interconnected with one another by flexible conductors embedded in insulation layers that can also be flexed. See, for example, the Haas Patent 5,121,297. There is no teaching in this patent, however, of having the substrates on which circuit components are mounted in other than a coplanar relationship.
The Karabatsos Patent 5,949,657 describes an electronic assembly comprising a number of rigid substrates or panels that are connected by flexible wired jumpers, allowing the multiple boards to be folded so as to be non-coplanar. The ""657 patent does not address problems brought about by close proximity of circuit components upon the folding of the assembly as far as EMI is concerned.
Thus, a need exists for a printed circuit assembly that allows for a relatively high component density, the ability to populate the printed circuit panels with components using only a single pass with automated pick-and-place equipment and which incorporates requisite shielding to prevent noise-generating circuits from adversely affecting operation of other components comprising the overall circuit assembly. The present invention meets these needs and provides other advantages and improvements that will be evident to those skilled in the art upon review of the following description and drawings.
The present invention provides a packaging approach that utilizes a plurality of printed circuit panels interconnected by flexible interconnecting flat cabling so that components may be mounted on one major surface of the panels only. Thus, only a single pass with pick-and-place equipment is require to populate the panels which then may be juxtaposed in non-coplanar relationship by folding the flexible interconnecting cabling. During initial component layout, consideration is given to component placement so that noise-generating components will not be closely proximate other components that may be sensitive to such noise following the folding thereof. Further, by including conductive shield structures in the printed circuit board, and by folding the assembly so that the components face outward, the shielding layers will be interdispersed with the active and passive components, thereby further reducing radio frequency interference and noise. The configuration also allows for the direct connection of ancillary components, such as batteries and capacitors, thereby reducing the inter-complexity and the cost of manufacture.